When packaging meat or other perishable products, it is often desirable to enclose the product in a preservative environment. For example, when packaging meat, it may be desired to provide an N.sub.2 --CO.sub.2 atmosphere in the container to prolong the shelf-life of the meat. However, when meat is packaged in N.sub.2 --CO.sub.2, it may turn an unappealing purple color due to a lack of oxygen in the surrounding gas. It is known that this coloring effect may be countered by removing the oxygen-poor environment and replacing it with an oxygen-rich atmosphere, which allows the meat to "bloom" and return to its more visually appealing red color before the meat is shelved and displayed to customers.
When carrying out this gas exchange procedure, it has been found to be more effective when a substantial portion of the oxygen-poor gas is removed prior to the introduction of the replacement gas. The oxygen-poor gas may be extracted by drawing a vacuum within the meat container. However, the pressure differential between the container and the container environment may cause the container to rupture or collapse during evacuation. Accordingly, it is desirable to control the pressure around the container during gas exchange. In this manner a corresponding vacuum may be drawn in the surrounding environment during gas exchange, thereby effectively nullifying the large pressure differential between the container and its environment. This procedure has been found to protect the container from pressure damage.
The use of an apparatus to exchange a first gas within a container for a second gas is known. For example, U.S. Pat. No. 4,919,955 to Mitchell discloses a method and apparatus for packaging perishable products. The invention disclosed therein comprises a relatively rigid tray which is sealed with a flexible gas impermeable cover, the tray being provided with a resealable septum valve. The tray is also preferably provided with a plurality of protrusions or mounds to facilitate gas flow and gas contact with the packaged product. Furthermore, U.S. Pat. No. 5,481,852 to Mitchell discloses a vacuum chamber provided with a means to align a sealed receptacle such that a gas exchange probe may be inserted into the receptacle through a resealable valve. The gas exchange probe establishes flow communication between the interior of the receptacle and a vacuum chamber. A vacuum is then drawn in the chamber, and the interior of the receptacle is evacuated through the flow probe. The coordinated vacuums help to prevent the distortion or collapse of the flexible receptacle.
While the apparatus disclosed in U.S. Pat. No. 5,481,852 is useful in performing the gas exchange process, there are numerous drawbacks in the apparatus which make it undesirable for commercial use.